Method for controlling the electric motor of a metering pump

ABSTRACT

The methods serves for activating an electric motor of a metering pump with which the fluid quantity (V nom ) to be delivered is set by an external impulse trigger, wherein a predetermined delivery quantity (V nom ) is allocated to each impulse (t). The control detects the temporal interval (Δt) of the two last-received impulses and activates the electric motor such that the fluid quantity to be delivered, taking the previously evaluated interval as a basis, is distributed over the subsequent impulse interval.

BACKGROUND OF THE INVENTION

[0001] The invention relates to a method for activating an electricmotor of a metering pump according to the features specified in thepreamble of claim 1.

[0002] Metering pumps functioning according to the displacementprinciple, thus those with a diaphragm or piston pump, are eitheroperated electromagnetically or by way of a motor. Withelectromagnetically operated metering pumps the delivery quantity isusually set by mechanical stroke adjustment on the one hand and byfrequency change on the other hand. In order to achieve as accurate aspossible metering (admixing) of the fluid into a changeable deliveryflow (main delivery flow) such pumps usually have an electricalconnection to which a clock generator may be connected which alwaysemits an impulse when a certain delivery quantity of the main deliveryflow has been delivered, whereupon the metering pump executes one ormore working strokes whose delivery stroke is mechanically matched tothe metering quantity to be dispensed per impulse. In spite of thismatching of the delivery flows to be mixed, irregular mixing ratios mayoccur depending on to the stoke adjustment and the fluid quantity to bedelivered, specifically if for example in a short time the fluid to bemetered is be delivered into the main flow and the next impulse is onlyeffected after a long period of time.

[0003] Besides metering pumps with an electromagnetic drive constructedwith quite a simple design, there are also known those with anelectromotoric drive, for example from DE 196 23 537 A1. Such meteringpumps are much more complicated with regard to design, but permit a moreexact and uniform control of the delivery quantity. Usually theyfunction without stroke adjustment. A metering pump of this constructiontype is for example known from the type LEOW A LAB K3/K5 of LEWA HerbertOtt GmbH & Co. in Leonberg. Although this pump comprises an interfacefor the external metering flow control, here however the activation iseffected via an analog signal, which is complicated in signal processingand further processing, and is also prone to malfunctioning. Themetering delivery quantity here is controlled in dependence on anelectrical current.

BRIEF SUMMARY OF THE INVENTION

[0004] Against this state of the art it is the object of the presentinvention to design an electromotorically driven metering pump such thatwith an external impulse activation it delivers according to apredefined course as exactly as possible.

[0005] According to the invention this object is achieved by thefeatures specified in claim 1. Advantageous formations of the methodaccording to the invention are specified in the dependent claims as wellas the subsequent description.

[0006] The basic concept of the present invention is to distribute thequantity to be delivered according to a predefined course over the timeinterval formed between two or more impulses, and specifically in amanner such that where possible there is always present a certaindelivery quantity. Usefully, at the same time, the temporal interval oftwo successive impulses is determined and then the drive of the electricmotor, for example a stepper motor or a direct current or alternatingcurrent motor equipped with suitable sensorics for position detection,is activated such that e.g. there is effected as uniform as possibledistribution of the fluid quantity to be delivered in the impulseinterval subsequent to this or in a subsequent impulse intervalsequence. Within the context of the present invention as uniform aspossible is to be understood for example in that with a stepwiseoperation the steps are distributed over the impulse interval with thesame temporal interval. It is to be understood that a completely uniformdistribution may possibly be upset by one or more required returnstrokes of the pump, even if, as already belongs to the state of theart, the motor during the return stroke is activated at a higher speedthan during the delivery stroke

[0007] If the temporal intervals between the successive impulses becomeshorter, this may lead to the fact that the delivered and metered fluidquantity is smaller that the actually desired quantity. In order toavoid this the invention envisages determining the missed quantityresulting after the activation of two or more successive impulseintervals and correcting this in a later, preferably in the subsequentimpulse interval. Such a correction may be effected in a comparativelymore complicated manner by determining the actual metering delivery flowby way of external sensorics, but is advantageously determined takingthe theoretical metering delivery flow resulting on account of theactivation as a basis, since then no external sensorics are required andthis may be determined by way of the electrical values which in any caseare present internally. Since electromotorically operated metering pumpsdue to their design operate accurately in comparison to the initiallydescribed electromagnetically operated ones, as a rule one may do awaywith external sensorics without having to accept the risk of seriousdisadvantages.

[0008] A particular advantage of the impulse control according to theinvention is the ability to do away with the stroke adjustment of thepump body known with pump membranes since this leads to inaccuracies anddemands a mechanical intervention which makes the remote control of thepump difficult.

[0009] In particular on admixing a fluid into a changing main deliveryflow it is desirable where possible not to let corrections take place atall, but to adapt the metering delivery flow as quickly as possible tothe changing main delivery flow. This may be effected in that with thedistribution of the fluid quantity to be delivered one does not onlytake into account the interval between two or several preceding impulsesand distribute this over a following impulse interval resultingtheoretically there from, but that with this also the change in theimpulse intervals is determined and taken into account when calculatingthe distribution, i.e. a certain control algorithm is effected whichachieves as early as possible adaptation to the changing conditions.

[0010] In particular, with metering procedures with which although onthe one hand it is a question of as uniform as possible supply to a maindelivery flow and on the other hand of the totally added quantity. i.e.a concentration to be set, as is for example required on admixingchlorine into swimming pool water, it is not only necessary to payattention to a uniform mixture ratio but also to exclude the addition oferrors which may possibly arise due to control inaccuracies or othersources of errors. For this the method according to the inventionenvisages detecting the number of impulses, i.e. the nominal deliveryquantity or a corresponding characteristic variable and comparing thisto the metering delivery quantity which results at least theoreticallyon account of the activation of the electric motor, or to acorresponding characteristic variable, and with differences envisagessubsequently compensating these accordingly. Such a long-term controlmay for example detect the impulses over hours or days in order once perhour or once a day, where appropriate to carry out a supplementarycorrection which may not be fulfilled by a quick control which adaptsthe delivery flow of the metering pump to the changing main deliveryflow.

[0011] Irrespective of this long-term control it is basically desirableto carry out the correction of the detected missed quantity directlyafter detection in order to ensure as quick as possible control. This isparticularly desirable if the metering pump is applied for thecontinuous admixing with which a filling or packaging is effecteddirectly after the admixing, so that later correction no longer have anyinfluence on the already filled or packaged product.

[0012] In order to ensure that also at the beginning of the meteringprocedure there is already effected a uniform metering over the wholeimpulse interval, it is useful to initiate the activation of the pumpmotor not until after the receipt of two impulses. The missed quantitycaused by the method because of this may be compensated by thepreviously described overriding correction control.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] The invention is hereinafter described in more detail by way ofone embodiment example. There are shown in:

[0014]FIG. 1: the dependency of the pulse sequence on the deliveryquantity of a first embodiment example and

[0015]FIG. 2: a second embodiment example in a representation accordingto FIG. 1,

DETAILED DESCRIPTION OF THE INVENTION

[0016] In the drawings on the upper time axis there is represented asequence of electrical impulses t₁ to t₇, as for example are emitted bya clock generator, wherein each impulse t₁ to t₇ stands for a certainvolume of a main delivery flow to which a suitable quantity of ametering delivery flow is to be admixed by way of the metering pump. Onthe lower time axis there is shown in each case the metering deliveryflow controlled by the metering pump in dependence on the externalimpulses.

[0017] In order to achieve as uniform as possible metering of themetering delivery flow into the main flow, the metering delivery flow isset by way of the control of the metering pump such that the meteringdelivery quantity to be mixed into the main flow is distributed asuniformly as possible over the whole interval Δt formed between twosuccessive impulses. In order to firstly detect the temporal intervalΔt, it is necessary before the beginning of the metering procedure towait for two electrical impulses t₁ and t₂ and to determine the timeΔt₁₂ lying between these. Then the pump is activated according to themetering delivery quantity to be admixed per impulse such that thevolume V_(nom) to be delivered per impulse is distributed over a timebeginning at t₂, which corresponds to Δt₁₂, so that taking this timeinterval Δt₁₂ as a basis there results a delivery flow Q₂₃ which hasreached the preset volume V_(nom) after a delivery time of Δt₁₂. Sincein the present embodiment example the interval of the impulses t₁ to t₄increases, with this control, with an increasing interval interval up tot₄ in each case a stoppage of delivery arises for a short time, ifspecifically the volume V_(nom) has already been reached, but thesubsequent impulse however has not been received.

[0018] If the control obtains the impulse t₃, it determines the temporalinterval Δt₂₃ to the impulse t₂ and now distributes the quantity V_(nom)to be delivered over this time interval Δt₂₃, thus reduces the deliveryflow Q₃₄ accordingly. The metering delivery flow Q₃₄ results in that onedivides the nominal delivery volume V_(nom) by the last-determined timeinterval Δt₂₃.

[0019] If the intervals of the impulses do not become larger, butsmaller, as this is represented by way of the impulses t₄ to t₆, therearises the problem that a new impulse, for example t₅ is received if thetime interval for which the delivery flow Q₄₅ has been calculated inorder to reach the volume V_(nom) is not yet completed. With the controlaccording to the first embodiment example (FIG. 1) the pump is activatedsuch that on receipt of a new impulse (here t₅ for the first time) theprevious delivery is stopped and for the now newly beginning deliveryinterval Δt₅₆ one fixes a delivery flow Q₅₆ which is calculated suchthat within a time period of At₄₅ there results a volume V_(nom) plus avolume V_(rest). The volume V_(rest) results from the volume V_(nom)minus the volume V_(ist) which is actually delivered in the precedinginterval. Thus for the delivery interval Δt₄₅ there results a volumeV_(rest) which results from the delivery flow Q₄₅ multiplied by thedifference of Δt₃₄ and Δt₄₅. This volume which is delivered in the timeinterval Δt₄₅ and which is too low thus is added to V_(nom) oncalculation of the delivery flow volume Q₅₆.

[0020] Since the time interval Δt₅₆ again is smaller than the precedingΔt₄₅, the delivery flow Q₅₆ is interrupted after receipt of the impulset₆ and then a metering delivery flow Q₆₇ is produced, with which takinga delivery interval of the size order of Δt₅₆ as a basis the deliveryflow has been calculated such that there results a volume whichcorresponds to the volume V_(nom) plus the volume V_(rest56) not yetdelivered in the delivery interval Δt₅₆. The volume V_(rest56) which hasnot yet been delivered at the same time is composed on the one hand of acomponent of the volume V_(nom) which has not yet been delivered in thisinterval and on the other hand of the not yet delivered component of thevolume V_(rest45) of the further preceding interval, which can berecognised by the cross-hatching whilst the remaining rest volume issimply hatched.

[0021] The previously described control algorithm illustrates the factthat by way of the control one may react quite quickly and exactly tothe impulse even with changing intervals. In practise the fluctuationsof the impulse intervals are quite low so that the comparativelycomplicated control represented by way of FIG. 1 is often not at allrequired or may be compensated by an additional overriding correction.Such an overriding correction may follow after a predefined time orafter a predefined number of impulses, wherein the nominal volume to bedelivered within this time corresponding to the impulse number isevaluated and compared to the actual volume resulting on account of thecontrol, and where appropriate is corrected in the subsequent intervalor in the subsequent intervals. Control errors or also controldeviations may be detected over this long-term correction in order toanticipate as much as possible the adaptation to the changing impulseintervals. In practise control errors, be they due to return strokes orother false strokes, may occur which otherwise are difficult to detector may not be detected at all.

[0022] In most cases however a simplified control according to theembodiment example according to FIG. 2 would be sufficient with whichthe delivery flow is computed according to the previously describedembodiment variant in which firstly one waits for two impulses t₁ andt₂, the time period Δt₁₂ formed between this is evaluated and thenominal volume V_(nom) to be delivered per impulse is distributed overthis time period A₁₂ so that a delivery flow Q results. In contrast tothe previously described embodiment variant however after reaching thedelivery flow V_(nom) the delivery procedure is not interrupted but onedelivers further up to the receipt of the next impulse t₃ in order toensure a continuous admixture. The delivery quantity Q₃₄ activated onreceipt of the impulse t₃ results from the volume V_(nom) to bedelivered per impulse and the time Δt₂₃. The delivery here is alsoeffected up to the receipt of the next impulse t₄.

[0023] As results from this, due to the control, with this embodimentvariant with a reducing impulse sequence too much is delivered, whilstwith an increasing impulse sequence too little is delivered, since ineach case the preset delivery quantity is not corrected until receipt ofthe next impulse. Since the main delivery flow in practice iscomparatively constant and the deviations fluctuate above and below tothe same extent, one may achieve a comparatively exact metering withthis simplified control with the advantage that one admixescontinuously, thus without breaks. Here too one may provide anoverriding control which for example counts the received impulses afterhours or days, determines the nominal volume of the whole meteringdelivery flow from this and compares this to the actual meteringdelivery flow delivered according to the control and where appropriatecorrects this. The overriding correction may advantageously be carriedout after a few impulses or after carrying out one or more pump strokes.Furthermore the control has the usual safety circuits which for exampleensure that the metering delivery flow is adapted given excessivelylarge deviations in the main delivery flow, e.g. is stopped if after apredefined time one receives no further impulse.

1. A method for activating an electric motor of a metering pump, withwhich the fluid quantity to be delivered is predefined by way of anexternal impulse trigger, wherein a predetermined delivery quantity isallocated to each impulse, characterised in that the temporal intervalof at least two impulses is detected and the electrical motor isactivated such that the fluid quantity to be delivered, taking thepreviously evaluated interval as a basis, is distributed over asubsequent impulse interval according to a predefined course.
 2. Amethod according to claim 1, characterised in that the temporal intervalof the at least two last impulses are detected and that the fluidquantity to be delivered, taking the previously evaluated interval as abasis, is distributed over the impulse interval following this asuniformly as possible.
 3. A method according to one of the precedingclaims, characterised in that missed quantity resulting after theactivation of two or more successive impulse intervals is determined andcorrected.
 4. A method according to one of the preceding claims,characterised in that the missed quantity resulting after the activationof two or more successive impulse intervals is determined and correctedin the subsequent impulse interval.
 5. A method according to one of thepreceding claims, characterised in that the temporal change of theimpulse interval is detected and the distribution of the fluid quantityto be delivered over one or more impulse intervals following this iseffected in dependency on this change.
 6. A method according to one ofthe preceding claims, characterised in that the number of impulses orthe fluid quantity to be delivered as well a delivery quantity resultingtheoretically on account of the activation or correspondingcharacteristic parameters are summed and stored, and that after apredetermined time the summed and stored values of the delivery quantityare compared to the fluid quantity to be delivered and where appropriatea correction of the delivery quantity is carried out.
 7. A methodaccording to one of the preceding claims, characterised in that the pumpmotor is not activated in delivery until the receipt of two impulses. 8.A method according to one of the preceding claims, characterised in thatthe correction procedure is effected directly after the detection,preferably in the impulse interval subsequent to the detection interval.